Integrated optical devices for directly processing optical signals have become of greater importance as optical fiber communications increasingly replace metallic cable and microwave transmission links. Integrated optical devices can advantageously be implemented as silicon on insulator (SOI) optical circuits having compact dimensions at relatively low cost. SOI optical circuits employ integrated waveguide structures formed in the silicon layer of the SOI substrate.
In some applications, optical gratings are formed in the SOI substrate or chip for input-output of the photonic signal. Typically, the optical grating is formed on a major surface of the substrate. Hence, the photonic signal path extends largely perpendicular to the SOI layer. When using the substrate in coupling applications, such as when coupling to an optical fiber, the optical fiber is typically mounted in near perpendicular fashion. The shape and pattern of the optical grating defines the wavelength response of the optical grating.